Modern aircraft operate at altitudes at which there is insufficient oxygen to sustain normal human conscious activities. A recent National Transportation Safety Board Aircraft Accident Brief (NTSB/AAB-00/01 at 6, fn 11) provides background information on this topic:                Pressurized aircraft cabins allow physiologically safe environments to be maintained for flight crew and passengers during flight at physiologically deficient altitudes. (At altitudes above 10,000 feet, the reduction in the partial pressure of oxygen impedes its ability to transfer across lung tissues into the bloodstream to support the effective functioning of major organs, including the brain. These altitudes are typically referred to as “physiologically deficient altitudes.”) At cruising altitudes, pressurized cabins of turbine-powered aircraft typically maintain a consistent environment equivalent to that of approximately 8,000 feet by directing engine bleed air into the cabin while simultaneously regulating the flow of air out of the cabin. The environmental equivalent altitude is referred to as “cabin altitude.”        
Current rules of operation for Transport Category airplanes, Federal Aviation Regulation (hereafter referred to as “FAR”) 121.333, require a pilot to don and use an oxygen mask whenever the airplane is above 25,000 feet and the pilot is alone on the flight deck and require at least one pilot to don and use oxygen at all times when the airplane is above 41,000 feet.
Similarly, for pressurized commuter and on demand aircraft operations, FAR 135.89 require a pilot to don and use an oxygen mask whenever the airplane is above 25,000 feet and the pilot is alone on the flight deck, and require at least one pilot to don and use oxygen at all times when the airplane is above 35,000 feet.
These requirements exist because external air pressure at cruise altitude is below the oxygen pressure in the pilot's bloodstream. In the event the cabin lost pressurization, the pilot would rapidly lose consciousness due to hypoxia. The “time of useful consciousness” following a loss of pressurization is shown in Table 1 below.
TABLE 1
Source of Table 1: “Physiologically Tolerable Decompression Profiles for Supersonic Transport Type Certification,” Office of Aviation Medicine Report AM' 70-12, S. R. Mohler, M.D., Washington, D.C.; Federal Aviation Administration, July 1970.
An oxygen mask provides a means of supplying 50% or 100% oxygen to the pilot at ambient or near-ambient pressure. Oxygen naturally comprises 21% of the air which, at 15,000 ft., exerts a partial pressure of approximately 1.74 psi. As shown in Table (1) above, the same partial pressure may be provided at 35,000 ft with 50% oxygen, or above 40,000 ft with 100% oxygen (see “Ambient pressure” column above). This is how an oxygen mask provides an extended time of useful consciousness in an unpressurized aircraft at cruise altitudes.
During a decompression event at high altitudes, it is conceivable a single pilot, trying to handle an emergency unassisted, could lose consciousness before he or she would be able to don an oxygen mask. Thus the requirement to wear an oxygen mask for any pilot alone on the flight deck.
Even with the development of quick-donning oxygen masks, the brief time between a rapid loss of aircraft cabin pressure and the donning and activation of an oxygen mask may be too long to ensure adequate oxygen for the pilot to safely control the aircraft and avoid losing consciousness. As noted by the NTSB: “Research has shown that a period of as little as 8 seconds without supplemental oxygen following rapid depressurization to about 30,000 feet may cause a drop, in oxygen saturation that can significantly impair cognitive functioning and increase the amount of time required to complete complex tasks.” NTSB/AAB-00/01 at 34. However, during a rapid decompression event, it is important to prevent an excessive pressure differential between the crew area (e.g., the cockpit) and the rest of the aircraft, to prevent structural damage to the aircraft. For this reason, a pressure equalization panel may be mounted between the crew area and an aircraft main cabin.
Accordingly, there is a need for improved systems for ensuring an oxygen supply to aircraft crew members in the event of a sudden loss of cabin pressure in an aircraft. The present invention is directed to overcoming one or more of the problems or disadvantages associated with the prior art.
This invention provides apparatuses and methods for maintaining pressure in an aircraft flight crew area, and/or re-pressurizing the flight crew area during and/or after a depressurization event, in order to extend the time of useful consciousness after a decompression, e.g., due to a breach of an aircraft door or fuselage structure.
In accordance with one aspect of the invention, an aircraft includes a flight crew area, at least one pressure sensor for detecting the pressure of the atmosphere within the flight crew area, and at least one regulated decompression panel that is operatively associated with the pressure sensor, for regulating the pressure within the flight crew area after a decompression event.
In accordance with another aspect of the invention, a method of extending the time of useful consciousness of a crew of a pressurized aircraft during and/or after a decompression event is provided. The method includes: providing a crew area; providing a pressure sensor adapted to detect the pressure of the atmosphere within the crew area; sensing pressure of the atmosphere within the crew area using the pressure sensor; and regulating the decompression of the atmosphere within the crew area when the pressure of the atmosphere within the crew area has fallen below a predetermined level.
In accordance with yet another aspect of the invention, a system is provided for extending the time of useful consciousness of a crew of a pressurized aircraft during and/or after a decompression event. The system may include a crew area, a pressure sensor adapted to detect the pressure of the atmosphere within the crew area, and an electronic controller linked to the pressure sensor. The electronic controller may be programmed to regulate the decompression of the atmosphere within the crew area when the pressure of the atmosphere within the crew area has fallen below a predetermined level.
In accordance with another aspect of the invention, a source of air and/or oxygen may be provided for re-pressurizing the crew area after a decompression event.
The features, functions, and advantages may be achieved independently in various embodiments of the present invention or may be combined in yet other embodiments.
Following a decompression event in a pressurized aircraft, the time of useful consciousness of the aircraft crew may be extended by preventing the pressure around the crew from dropping all the way to ambient levels, or by combining increased pressure with increased oxygen.
This invention provides several systems and methods to extend the time of useful consciousness of a pilot or other crewmember in an occupied compartment, such as, for example, a flight deck.
FIG. 1 illustrates one possible layout of a pressure regulation system 10 according to one aspect of the invention. One or more crewmembers may be contained within a crew area 12 (such as in a flight deck or a crew rest compartment), separated from the rest of a pressurized aircraft fuselage 14.
The walls of the crew area 12 may be designed to withstand some maximum pressure differential, PSTR, which is approximately 2 psi for many existing airplanes. Of course, PSTR may be higher or lower than 2 psi, depending on the specific design and construction of the crew area 12. In the event of some structural penetration 17 in the fuselage 14, the fuselage area will rapidly decompress. A mechanical decompression panel assembly 22 may be used to keep the pressure in the crew area 12 below PSTR, thereby maintaining the integrity of the walls of the crew area 12.
A first pressure differential, ΔP1, between pressure in the crew area 12, PCA, and the ambient pressure outside the aircraft, PA, may be measured by a first pressure sensor 11. A second pressure differential, ΔP2, between the crew area pressure, PCA, and the pressure, PF, in adjacent areas of the aircraft fuselage 14, may be measured by a second pressure sensor 13. Additionally, the position of a decompression panel 24 (FIG. 2) in the decompression panel assembly 22 may be monitored. These signals may be fed to an electronic controller 18.
As shown in FIG. 2, the decompression panel assembly 22 may be further fitted with a shutter 25, and an actuator 21, connected to the electronic controller 18. The shutter 25 may be closed partway through a decompression event to maintain pressure within the crew area 12 by sealing off the crew area 12, thereby extending the time of useful consciousness of the occupants.
With reference to the logic diagram in FIG. 3, the electronic controller 18 may detect a decompression event by a sufficiently rapid change in ΔP1, PCA, ΔP2, and/or by detecting the decompression panel 24 opening, as indicated at 30 and 32. After detecting the decompression event at 34, the electronic controller 18 monitors ΔP1 at 36 and 38, until this pressure falls below PSTR. At this point, the controller may command triggering of the actuator 21, which causes shutter 25 to close as indicated at 40, preventing further airflow through the decompression panel assembly 22.
This action reduces the rate of depressurization of the crew area 12, thereby extending the time of useful consciousness for the occupants. Sealing other leakage paths further reduces the rate of depressurization.
In accordance with another aspect of this invention, a gas cylinder 26 may be connected to and activated by the controller 18 such that air leaking from the crew area 12 may be continuously replenished, maintaining the pressure within the crew area 12, further extending the time of useful consciousness. Significantly greater extensions of time of useful consciousness may be attained if the gas in cylinder 26 is oxygen-enriched air, or pure oxygen.
Protection from a gradual loss of pressurization event may be achieved by monitoring ΔP1, or PCA, such that when either pressure falls below a preset level, the shutter 25 in assembly 22 closes. As above, a gas cylinder may be used to maintain the pressure within the crew area 12. For example, as shown in FIG. 5, the electronic controller 18 detects a gradual loss of pressurization by monitoring PCA, as indicated at 54 and, as indicated at 56 checking whether PCA is less than a threshold absolute pressure, such as, for example 8 psia. If a gradual loss of pressurization has occurred the decompression panel 24 will remain closed, as indicated at 58, because ΔP2≈0. Then, as indicated at 60, the controller may command the actuating panel to close and the crew area 12 to be repressurized.
In another embodiment of this invention, the crew area 12 may be allowed to entirely depressurize before the shutter 25 in assembly 22 is closed, after which the volume is repressurized with air, oxygen-enriched air, or oxygen from gas cylinder 26. For example, as indicated at FIG. 4, the electronic controller 18 detect a decompression event by a sufficiently, rapid change in ΔP1, PCA, ΔP2, and/or by detecting the decompression panel 24 opening, as indicated at 42 and 44. After detecting the decompression event at 46, the electronic controller 18 monitors ΔP1 to see whether it is approximately 0, as indicated at 48 and 50. If ΔP1 is approximately 0, decompression is completed, and the electronic controller 18 will close the actuating panel and initiate repressurization of the crew area 12, as indicated at 52.
This method could make use of the decompression panel 22 illustrated in FIG. 2 or a similar panel that, can be rapidly opened and closed. Further, electronic controller 18 might be replaced by a pneumatically operated mechanical controller or other equivalent device.
Other aspects and features of the present invention can be obtained from a study of the drawings, the disclosure, and the appended claims.